diff --git a/package/inc/ZipFile.hxx b/package/inc/ZipFile.hxx
index b2f3e6ecf131..8828d929273f 100644
--- a/package/inc/ZipFile.hxx
+++ b/package/inc/ZipFile.hxx
@@ -30,6 +30,7 @@
 #include "EncryptionData.hxx"
 
 #include <span>
+#include <unordered_set>
 
 class MemoryByteGrabber;
 namespace com::sun::star {
@@ -50,10 +51,13 @@ namespace rtl
 
 class ZipEnumeration;
 
+
 class ZipFile
 {
     rtl::Reference<comphelper::RefCountedMutex> m_aMutexHolder;
 
+    std::unordered_set<OUString> m_EntriesInsensitive;
+
     EntryHash       aEntries;
     ByteGrabber     aGrabber;
     ZipUtils::Inflater aInflater;
diff --git a/package/source/zipapi/ZipFile.cxx b/package/source/zipapi/ZipFile.cxx
index fa8d74b37b80..f7713b8665c1 100644
--- a/package/source/zipapi/ZipFile.cxx
+++ b/package/source/zipapi/ZipFile.cxx
@@ -94,6 +94,7 @@ ZipFile::ZipFile( rtl::Reference<comphelper::RefCountedMutex> aMutexHolder,
     if (bInitialise && readCEN() == -1 )
     {
         aEntries.clear();
+        m_EntriesInsensitive.clear();
         throw ZipException( u"stream data looks to be broken"_ustr );
     }
 }
@@ -118,6 +119,7 @@ ZipFile::ZipFile( rtl::Reference< comphelper::RefCountedMutex > aMutexHolder,
         else if ( readCEN() == -1 )
         {
             aEntries.clear();
+            m_EntriesInsensitive.clear();
             throw ZipException(u"stream data looks to be broken"_ustr );
         }
     }
@@ -1156,15 +1158,19 @@ sal_Int32 ZipFile::readCEN()
                     continue; // This is a directory entry, not a stream - skip it
             }
 
-            if (auto it = aEntries.find(aEntry.sPath); it == aEntries.end())
-            {
-                aEntries[aEntry.sPath] = aEntry;
-            }
-            else
+            if (aEntries.find(aEntry.sPath) != aEntries.end())
             {
                 SAL_INFO("package", "Duplicate CEN entry: \"" << aEntry.sPath << "\"");
                 throw ZipException(u"Duplicate CEN entry"_ustr);
             }
+            // this is required for OOXML, but not for ODF
+            auto const lowerPath(aEntry.sPath.toAsciiLowerCase());
+            if (!m_EntriesInsensitive.insert(lowerPath).second)
+            {
+                SAL_INFO("package", "Duplicate CEN entry (case insensitive): \"" << aEntry.sPath << "\"");
+                throw ZipException(u"Duplicate CEN entry (case insensitive)"_ustr);
+            }
+            aEntries[aEntry.sPath] = aEntry;
         }
 
         if (nCount != nTotal)
@@ -1335,6 +1341,12 @@ void ZipFile::HandlePK34(std::span<const sal_Int8> data, sal_Int64 dataOffset, s
                != aEntries.end())
         return;
 
+    auto const lowerPath(aEntry.sPath.toAsciiLowerCase());
+    if (m_EntriesInsensitive.find(lowerPath) != m_EntriesInsensitive.end())
+    {   // this is required for OOXML, but not for ODF
+        return;
+    }
+    m_EntriesInsensitive.insert(lowerPath);
     aEntries.emplace(aEntry.sPath, aEntry);
 
     // Drop any "directory" entry corresponding to this one's path; since we don't use